Some pneumatic tires have a tread portion formed from a belt layer and a carcass layer in which steel cords are coated with a coating rubber (rubber composition for coating steel cords). As adhesiveness between these steel cords and the rubber member is reduced as a result of use for a long period of time, failure tends to occur, and tire durability tends to deteriorate. However, in recent years, the period of use of a tire tends to be longer, and it becomes more important to enhance reinforcing effect by the steel cords and to maintain durability for a long period of time.
Japan Unexamined Patent Publication No. 2007-099868 proposes to enhance adhesiveness to steel cords by a rubber composition containing organic acid cobalt salt in a diene rubber. However, even higher levels of improvement in adhesiveness to steel cords have been demanded by consumers.